Atherosclerosis is a widespread disease of the inner layers of arteries which results in regions of arterial narrowing and hardening, and the early detection of this disease prior to the appearance of overt symptoms is highly desirable to facilitate treatment.
A number of techniques are available for the measurement of arterial blood flow and thus the detection of atherosclerosis including electromagnetic, nuclear magnetic resonance, laser Doppler, X-ray with die injection, and ultrasonic Doppler techniques, the last providing the only method for noninvasive imaging of blood vessels.
Heretofore, however, Doppler ultrasound systems have not been capable of providing the desired velocity and spacial resolution in deep blood vessels, where many of the most harmful atherosclerotic lesions occur. Moreover, imaging deep blood vessels has previously required relatively high ultrasound exposure rates as the sensitivity of such systems is not sufficiently high. Accordingly, it is an object of the present invention to provide a novel ultrasonic flowmeter particularly suited for measuring blood flow which utilizes two pairs of crossed focused ultrasonic beams to provide improved sensitivity and velocity and range resolution.
It is also an object to provide such a flowmeter capable of measuring the three dimensional velocity vector of dynamic particles, particularly blood cells.
Another object is to provide such a flowmeter which is readily used in conjunction with a B-mode scanning device to provide information about the structure of and blood flow within a vessel.